1. Technical Field
The invention relates to touch detecting interactive displays. More particularly, the invention relates to methods and systems for determining the areas at which a user contacts a touch-detecting interactive display.
2. Description of the Prior Art
Many common tasks require one or more individuals to interactively explore information presented on a display. For example, a team of paleontologists may wish to discuss an excavation plan for a remote dig site. To do so, they wish to explore in detail the geographic characteristics of the site as represented on digitized maps presented on a display. Traditionally, this required the team to either huddle around a single workstation and view maps and images on a small display or sit at separate workstations and converse by phone. Collaborative exploration of the imagery is much more easily accomplished with the users surrounding a single large display. A particularly effective device is a touch detecting, interactive display, such as that disclosed in the referenced patent filing entitled “Touch Detecting Interactive Display”.
FIG. 1 shows several users operating a touch-detecting interactive display. The users 50 surround the display 100 such that each can view the display surface 150, which shows imagery of interest to the users. For example, the display may present Geographic Information System (GIS) imagery characterized by geographic 161, economic 162, political 163, and other features, organized into one or more imagery layers. Because the users can comfortably surround and view the display, group discussion and interaction with the display is readily facilitated.
Generally corresponding with the the display surface is a touch sensing region 155 monitored by a touch sensor capable of detecting when and where a user touches the display surface. Based upon the contact information provided by the touch sensor, user gestures are identified, and a command associated with the user gesture is determined. The command is executed, altering the displayed imagery in the manner requested by the user via the gesture. For example, in FIG. 1, a user 55 gestures by placing his fingertips on the display surface and moving them in an outwardly separating manner. In response, a zoom gesture is identified, and the imagery on the display is magnified.
A number of touch sensor technologies, operating on a variety of principles, have been proposed for detecting contacts within the touch sensing region. In one approach, a resistive touch pad is placed beneath a flexible display surface. The resistive touch pad comprises two layers of plastic that are separated by a compressible insulator such as air, and a voltage differential is maintained across the separated layers. When the upper layer is touched with sufficient pressure, it is deflected until it contacts the lower layer, changing the resistive characteristics of the upper to lower layer current pathway. By considering these changes in resistive characteristics, the location or locations of the contact can be determined. In another approach, surface acoustic waves (SAWs) passing above the surface of the touch sensing region are absorbed and reflected when a user contacts the display. Acoustic sensors analyze the altered sound field to determine the contact location or locations.
More commonly used are capacitive technologies, in which the touch sensing region is coated with a transparent conductor (e.g. indium tin oxide (ITO)). Contacting the coating with another conductor (e.g. a human finger or hand) induces a change in capacitance. In surface capacitance sensors, measurements of the capacitance at points on the perimeter of the touch sensing region allow the location of the contact to be determined. In projected capacitance sensors, a insulating grid is etched into the conductive coating, allowing for a grid of localized capacitance measurements and therefore improved accuracy in the determination of the contact location or locations.
The above touch sensor technologies, however, are not easily scaled to the very large display sizes that are desirable for use in the multi-user, collaborative scenario illustrated in FIG. 1. Moreover, manufacture of the touch sensor is both costly and deeply integrated with the manufacture of the display—the touch sensor cannot be easily retrofit to conventional displays.
Optical imaging system provide increased scalability, affordability, and versatility. Such systems typically incorporate one or more of light sources, light detectors, and retroreflectors arrayed on the perimeter of the touch sensing region. The touch sensor determines a contact area by analyzing the occlusion or reflection of light induced by objects (e.g. a human finger or hand) contacting the touch sensing region.
U.S. Pat. No. 4,144,449 to Funk et al. discloses one such system in which fluorescent light tubes arrayed on three sides of a rectangular touch sensing region emit light through narrow slits. Linear image detectors (e.g. CCDs) with 90° fields of view and positioned in the two corners opposing the fluorescent light tubes look for gaps in the bands of light emerging from the narrow slits. The location of a single contact area is determined by direct triangulation of the occluded portions of the field of view.
However, direct triangulation is not easily extended to multiple, simultaneous contact areas. As shown in FIG. 2, ambiguity can arise. The system disclosed by Funk, relying on two detectors 301 and 302, cannot disambiguate the pair of contact areas 311 from the pair of contact areas 312 or the single contact area 313. The introduction of additional sensors can aid in resolving the particular ambiguity shown in FIG. 2, but problems still arise when one contact area occludes another contact area as viewed by one of the detectors.